Automotive engine fans function to cool an engine by forcing air through the automotive engine radiator. Automotive engine fans also force air through air conditioning condenser coils. Automotive engine fans are normally driven by the automotive engine through a shaft extending from the water pump which is connected by a belt to the engine crankshaft. Electrically driven automotive engine fans have been developed to replace engine driven fans to allow operation independently of the automotive engine. Electrically driven fans add cost and weight to an automobile and are generally disfavored by automotive engineers.
Automotive design considerations including cooling efficiency, weight reduction, vehicle air flow resistance and styling have resulted in making it desirable to reduce the overall size of automotive fan and radiator assemblies. Higher efficiency automotive fans permit the use of smaller fans without a corresponding reduction in air flow capacity. Current styling preferences are moving towards providing smaller openings for air flow into the fan inlet area.
Engine vibration during normal operation and engine roll caused by starting and stopping the engine must be allowed for in engineering an automotive fan and shroud. Generally about one inch clearance is provided between the tips of the fan and the shroud. The shroud is normally body mounted and is generally unaffected by engine vibration and engine roll. Prior art automotive fan blade drive trains have not been positively attached to body mounted shroud assemblies by anti-friction bearings due to the need to accommodate engine vibration and roll.
Clearance between the fan tips and shroud dramatically reduce fan efficiency. This clearance also limits the maximum fan size permitted within space defined by the fan shroud. For example, if clearance between the fan tips and shroud is reduced from the normal one inch to one-half inch, then the fan diameter may be increased by one inch within the same fan shroud. Since air flow efficiency varies as a cube of the diameter of the fan blade, a larger fan diameter increases air flow substantially. For example, by replacing a 16 inch diameter fan with a 17 inch diameter fan results in about a 25% increase in air flow.
A long-standing objective in the development of automotive engine fans and shroud assemblies is the reduction of noise. A larger fan permits reduction in the speed of rotation of the fan for the same air flow levels. Reduction of the speed of rotation decreases the amount of noise caused by the automotive fan.
Normally, fan rotation must be limited to about 2,500 revolutions per minute. The speed of rotation of the water pump varies directly with the engine speed and on some vehicles may at times reach 9,000 revolutions per minute. Viscous clutches such as that disclosed in U.S. Pat. No. 4,238,015 disengage at high speeds and may include a temperature responsive element which disengages the automotive fan at low temperatures. When the fan is disengaged, the engine is allowed to heat up without significant cooling by the engine radiator.
A general application hydraulic shaft coupler is disclosed in U.S. Pat. No. 2,574,129 which accommodates angular shaft offsets and functions as a hydraulic universal joint. This hydraulic universal joint does not allow axially offset shafts to be coupled together in a driving relationship.
These and other problems relating to automotive fan drive assemblies are overcome by the present invention.